1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus using the same. The present invention can suitably be applied to a video camera, a digital camera, a television camera, a monitoring camera, and a film camera.
2. Description of the Related Art
With improvements in performance and functionality of image pickup apparatuses using solid-state image pickup elements, reduction in the overall apparatus size has been achieved in recent years. As image optical systems used in such image pickup apparatuses, zoom lenses having a high zoom ratio and excellent optical characteristics throughout the entire zoom range and small in overall size are required.
As zoom lens meeting the above requirements, there has been known a four-unit zoom lens composed of first to fourth lens units respectively having positive, negative, positive, and positive refractive powers in order from the object side to the image side, which are moved for zooming.
Japanese Patent Application Laid-Open No. 2009-098449 discloses a zoom lens of which the second lens unit is composed of three lenses and the third lens unit is composed of three lenses. This zoom lens has a zoom ratio of 21.0 and an angle of view of approximately 80 to 85 degrees at the wide angle end. Japanese Patent Application Laid-Open No. 2012-048033 discloses a zoom lens of which the second lens unit is composed of three lenses and the third lens unit is composed of four lenses. This zoom lens has a zoom ratio of 17.8 and an angle of view of approximately 90 degrees at the wide angle end.
To reduce the size of a zoom lens, it is preferred, typically, to increase the refractive powers of the lens units constituting the zoom lens, reduce the amount of shift of each lens unit with zooming, and to reduce the number of lenses in each lens unit. However, if the zoom lens is designed in this way, aberration variation with zooming will be increased, making it difficult to achieve excellent optical characteristics throughout the entire zoom range.
Therefore, to achieve reduction in the overall size of a zoom lens and high zoom ratio while keeping excellent optical characteristics, it is important to appropriately design the magnification variation provided by each lens unit in the zoom lens and the refractive power and the lens configuration of each lens unit.
For example, in the case of the above-described four-unit zoom lens, it is important to appropriately design the refractive power and the lens configuration of each of the lens units that move for zooming. It is particularly important to appropriately design the configuration of the third lens unit and the imaging magnification (lateral magnification) of the third lens unit at the wide angle end and at the telephoto end. If these factors are inappropriate, it is difficult to provide a zoom lens that is small in size and has excellent optical characteristics while having a high zoom ratio.